In-Ear Microphone Techniques for Severe Noise Situations

Today, noise reduction methods are nearly ubiquitous although often not noticed by laymen. Cellular phones, some hands-free headsets and ear-phones offered by some airlines during long haul flights all utilize noise reduction algorithms. However, there are some situations in everyday life where ordinary noise reduction algorithms do not suffice; situations where the surrounding noise sound pressure level is too high to be efficiently attenuated by ordinary algorithms. Personal communication is then partly or totally prohibited by this noise. Examples of such situations may be motorcycle riding or attending a concert. In addition, many occupations, foremost industrial work, expose people to very high sound pressure levels. Still, these people need to be able to communicate safely. This report describes a technique where an ear-mic, i.e. a small microphone for communication purposes, is placed inside the auditory canal where it picks up bone conducted speech from the user's speech organ. The report describes three different approaches and usage areas: First, a basic approach where combination effects of an ear-mic and a pair of Active Noise Control (ANC) equipped ear-muffs are investigated. Second, this approach is used to improve a speech recognition system. The third approach is to connect a well-known noise reduction algorithm - the spectral subtraction - in cascade with the previously described ear-mic/ANC-solution in order to achieve extreme noise suppression